1. Field of the Invention
This invention relates generally to fluid pressure responsive electric switches and methods for making them, and more particularly to certain specific features for making such switches more reliable with less variability from one switch to another and at lower cost.
2. Description of the Related Art
Devices for opening and closing an electric circuit in response to changes in values of fluid pressure by admitting the fluid pressure to one side of a rapid deflection actuator, such as a snap acting diaphragm, causing it to move from a first configuration to a second configuration at a predetermined actuation pressure value and return at another deactuation pressure value are well known. Typically, a motion transfer member is movably mounted adjacent to the actuator and adapted to transfer motion from the actuator to a movable arm of an electric switch.
A continuing need exists in the industry to improve the reliability of such switches and at the same time lower their unit costs. One area in which improvement is desired relates to providing switches which will more consistently operate within design specifications for actuation and deactuation pressure levels. Various prior art means have been devised to adjust or calibrate devices in order to obtain consistent actuation and deactuation from device to device. For example, the length of the motion transfer member can be selected to compensate for variations in distance between the actuator and the movable arm of the switch. In some devices the movable switch arm can be adjusted by varying the angle of a bracket mounting the arm. In some devices the position of the stationary contact of the switch can be adjusted by means of a threaded member aligned with the contact. Although such devices can generally be brought into a desired specification using such adjustment techniques they add to the cost of the switch by adding components in some cases and adding operations in others.
Another area in which improvement is desired is in providing an effective environmental seal which is of low cost and is conducive to mass manufacturing techniques. Various sealing techniques are disclosed in the prior art including the use of an outer housing in which the switch is disposed with epoxy infilled around the terminals extending from the switch as shown in U.S. Pat. No. 3,816,685. This technique is effective, however, it significantly adds to assembly time to allow for adequate curing. In addition, storage space is tied up while the epoxy is curing and special holding means is required for holding the switches during the curing period.